Aquila, and some other stars. But from this time forward, I propose to use the instrument in one position of the telescope, with the hope of ascertaining, if not the parallax of these stars, at least the limits, which it does not exceed.

Though the change of position in the telescope, by which all error of division is avoided, is one of the most beautiful properties of this instrument, yet so accurately is it divided, that I cannot perceive, with certainty, any effect produced by this change, for I have often found as great a discordance between two series of observations made on the same divisions, as when they are entirely changed by a new position of the telescope. What the error of division may amount to in any one position, I cannot exactly say; but, I think, when the six microscopes are used, it can never exceed half a second, and very rarely amounts to half that quantity.

That some opinion may be formed of the accuracy of this instrument, I have subjoined to the Catalogue the results of the observations of some of the standard stars, whose places I am anxious to determine with the greatest precision, since I propose in future to determine all north polar distances by comparison with these stars; precisely in the same manner as right ascensions are now determined by comparison with the thirty-six stars, whose places have been so accurately determined by Dr. MASKELYNe.

RESULTS OF OBSERVATIONS.

B Ursa Minoris.

1812, June 12, 13, 14, 16, 1749,659 Mean of 10 49,659

21, 22, 23, 28, 29

June 30, July 6, 8, 9, 18, 20, 21, 22, 28, Aug. 7

48,926 Mean of 20 49,292

48,996 Mean of 30 19,194

48,617 Mean of 40 19,049

Oct. 31, Nov. 9, 14, 18, 21, 22, 48,485 Mean of 50 48,937 23, Dec. 7, 8, 12

Dec. 14 1813 May 21, 26,

27, 28, 29, 31, June 1,4,748,951 Mean of 60 48,999

June 8, 11, 12, 16, 21, 22, 2549,695 Mean of 70 49,047 July 4, 5, 6,

July 9, 12, 16, 17, 18, 20, 22, 48,651 Mean of 80 48,998 24, 25, 26

July 28, 29, 30, Aug. 4, 7, 948,616 Mean of 90 48,955

12, 13, 16, 18

This result is probably exact to within a quarter of a second. The discordances seem quite accidental, they neither arise from parallax, nor error of division, for the three last series were made with the telescope in the same position, and consequently upon the same division, yet they differ more than observations usually do, which are made in different positions.